class Dog:
	
	def set_age(self,new_age):
		if new_age>=0 and new_age<=20:
			self.age = new_age
		else:
			self.age = 0
		
	def get_age(self):
		return self.age


dog = Dog()
# dog.age = 5
# print(dog.age)

# dog.name = '小白'

dog.set_age(-1)

age = dog.get_age()
print(age)


		
		